1. Field of Invention
The present invention relates to a method for manufacturing a liquid crystal display device. More specifically, the invention relates to a method for manufacturing a liquid crystal display device capable of preventing nozzle clogging and variations of spacers, and obtaining a liquid crystal display device having high display quality.
2. Description of Related Art
In a liquid crystal display device, spherical spacers are disposed between substrates, for maintaining a constant gap between the substrates. A technique for arranging the spacers can include spraying the spacers mixed in a solvent on a substrate subjected to an orientation treatment. However, this spraying device for disposing the spacers causes a nonuniform distribution of the spaces on the substrate. Particularly, when many spacers aggregate in a region (referred to as a pixel region) used for a display, brightness of coloration decreases, or uneven color occurs to cause the problem of deteriorating display quality.
In order to solve the problem, for example, Japanese Unexamined Patent Application Publication No. 11-281985 discloses a technique for discharging spacers from a droplet discharge apparatus to accurately arrange the spacers in a region (referred to as a non-pixel region (black matrix) hereinafter) not used for a display, improving a contrast of a liquid crystal display device. In this technique, the spacers are dispersed in a mixed solvent (boiling point 100° C. or more) of water and ethylene glycol, and the solvent is discharged to the non-pixel region of a substrate to arrange the spacers, and is further evaporated by heating the substrate to fix the spacers at a predetermined position. The substrate is heated to a substrate temperature of 60° C. or more for evaporating the solvent.
However, with a substrate temperature of 60° C. or more, the solvent evaporates in a long-term work (for example, 8 hours or more) to clog a nozzle tip with the spacers. Also, when spacers (referred to as adhesive spacers hereinafter) having adhesive surface layers are used, the adhesive layers are melted to further clog the nozzle with the spacers. Therefore, the spacers cannot be stably discharged to cause the problem of forming a portion in which the spacers are not disposed on the surface of the substrate.
On the other hand, with a low substrate temperature (for example, 30° C. or less), solvent droplets slowly evaporate when a mixture of spacers and a solvent is ejected onto the surface of the substrate by an ink-jet (droplet discharge) system, and thus the solvent spreads during a movement of the substrate to a next step, thereby causing the problem of deviating the spacers from the predetermined position.
Furthermore, in the use of the adhesive spacers, the solvent rapidly evaporates by heating the substrate to 60° C. or more, and thus an aggregation rate of the spacers is lower than an evaporation rate of the solvent, thereby causing the problem of failing to appropriately aggregate the spacers at the predetermined position of the non-pixel region. Furthermore, in the use of the adhesive spacers, the adhesive layers are melted by being heated to the substrate temperature before the spacers aggregate at the predetermined position, thereby causing the problem of possibly arranging the spacers in the pixel region.
Also, since the solvent is successively ejected onto the surface of the substrate by the ink-jet (droplet discharge) system, a time difference occurs between a first landing position and a last landing position on the substrate to cause a difference in evaporation time between both landing positions, thereby causing a difference in evaporation condition. Therefore, if the substrate is moved to a next step before the solvent does not sufficiently evaporate, the spacers do not aggregate at a center of the landing point to possibly cause a variation in arrangement of the spacers.